All phrases are relevant to all versions of XF. The version_string field just tells you when the phrase was created. You still need to translate all phrases.
The version_string can be useful for updating your language pack later on. You can look for new phrases since the previous version and translate only those new phrases when updating your language pack.
Hi there! Well, my mistake. It has only one phrase independently of the version. However it seems that when I generate the XML language file I'm getting several repeated lines. This is why I thought I had repeated phrases. What is the correct way of generating this file so it doesn't repeat the lines?